[clang] [llvm] [RISCV] Remove experimental XRivosVizip support (PR #200761)

[Kito Cheng via cfe-commits]

https://github.com/kito-cheng approved this pull request.

Another page has been turned in the history of RISC-V, LGTM.

https://github.com/llvm/llvm-project/pull/200761